This fixes several issues with 'StyleSheet' and simplifies the
implementation.
1. The generated style sheet could render after an apps existing style
sheets, potentially overwriting certain 'html' and 'body' styles. To fix
this, the style sheet is now rendered first in the document head.
2. 'StyleSheet' didn't make it easy to render app shells on the server.
The prerendered style sheet would contain classnames that didn't apply
to the client-generated style sheet (in part because the class names
were not generated as a hash of the declaration). When the client
initialized, server-rendered parts of the page could become unstyled. To
fix this 'StyleSheet' uses inline styles by default and a few predefined
CSS rules where inline styles are not possible.
3. Even with the strategy of mapping declarations to unique CSS rules,
very large apps can produce very large style sheets. For example,
twitter.com would produce a gzipped style sheet ~30 KB. Issues related
to this are also alleviated by using inline styles.
4. 'StyleSheet' didn't really work unless you rendered an app using
'AppRegistry'. To fix this, 'StyleSheet' now handles injection of the
DOM style sheet.
Using inline styles doesn't appear to have any serious performance
problems compared to using single classes (ref #110).
Fix#90Fix#106
